Heavy bulk materials such as sand, gravel, rocks, and the like must often be transported in a steady stream for loading vehicles, stockpiling, or transporting the bulk materials for processing. The typical conveyor includes a long, wide, endless belt often formed of fiber reinforced rubber. The flexible belts may be trained over conveyor rolls and driven about working and return flights that extend over substantial lengths.
Belts for bulk material conveyors are very expensive and time consuming to replace. Effort has therefore been directed to minimize wear along the belt surfaces to thereby extend the belt life to its maximum limit.
One approach at reducing belt wear has been to provide movable support beneath the working flight. U.S. Pat. Nos. 2,838,164, 2,865,494, and 2,821,290 to Duncan disclose rigid weight-bearing U-shaped transverse support members for supporting a conveyor belt. The support members are pivotally connected at opposite ends to wheels that ride along tracks. The pivotal connection between the wheels and support members allows the support members to maintain an upwardly facing concave orientation on both return and working flights. The individual support members are interconnected by a "cable chain" that allows motion of the support ends in three dimensions.
U.S. Pat. No. 2,727,617 to Thomson discloses a belt conveyor having an intermediate driving support for the conveyor belt. The intermediate support is comprised of a driven set of "endless cables" consisting of chains that are arranged on opposite sides of the belt. Each of the chains is led about a pair of sprockets, one of which is driven. Cross carriers bridge the two endless chain lengths and interrupt the links such that each chain is comprised of a number of short sections interconnecting the cross carriers. Wheels are mounted at the points of connection between the cross carriers and chain links.
A wheel is provided at each connection point on the Thomson conveyor so there is a total of four wheels rotatably mounted on each of the carriers. The connection arrangement requires that the wheels on each end of the cross carriers be spaced along the chain by a distance equal to the pitch of the chain. Since the wheels are of somewhat large diameter, the resulting requirement for chain pitch is substantial--in fact, the pitch is such that specialized end sprockets must be used.
The Thomson conveyor provides drive for the flexible conveyor belt through the chain connected cross carriages. To facilitate transmission of driving power from the carriers to the belt, both working and return flights are contacted by the carriers for driving purposes. The return flight of the conveyor belt is sandwiched between plates provided on the cross carriers and rollers on the conveyor frame. The belt therefore remains in contact with the cross carriers on the working flight and return flight. The weight of the chain and cross carriers rests against the belt along the return flight since there is no support otherwise provided.
U.S. Pat. No. 4,351,431 to Fenton discloses a heavy duty belt conveyor that makes use of typical wire or cast link chain connected carriers. The carriers extend across and under the working flight of the belt and flex according to the load carried thereby. Like the Thomson conveyor, the Fenton device includes a return flight that sandwiches the conveyor belt between the flexible cross carriers and return flight support rolls.
A somewhat similar arrangement is disclosed in U.S. Pat. No. 3,381,799 to Havelka. Here, however, the flexible conveyor belt is secured to the cross carrying frames and the frames are made up of pivotably connected rigid links.
U.S. Pat. No. 2,582,881 to Mitchell discloses an endless conveyor in which the load carrying capability of the working flight is enhanced by a number of interconnected carts, each having a pair of cradle members mounted thereon. The carts include concave surfaces for carrying the working flight of the conveyor belt. The belt is also carried along its return flight by surfaces on the carts opposite the concave surfaces. A complex end roll mechanism is provided for moving the conveyor belt into position above the carts along the return flight. The interconnected carriages are also linked together by a chain for driving purposes.
U.S. Pat. No. 4,378,875 to Allan, et al, discloses a "sling" form of belted bulk material conveyor in which belt carriers are fixed to the belt and are arranged to pivot between a sling cross configuration on the working flight and a straightened configuration on a return flight.
U.S. Pat. No. 826,312 to Catlin disclosed another form of belt wherein the driving cable for the conveyor is connected directly to the belt for support and drive.
U.S. Pat. No. 1,702,314 to Rankine discloses a belt conveyor and elevator wherein a number of carriages are connected together to form a chain link arrangement interconnected by cable. A complex roller mechanism is also shown for selectively engaging and disengaging wheel supported belt carriers. A roller chain driving mechanism is also provided, connecting the releasable roller units to the cable linked carriages.
Of the above apparatus, none are believed to provide an adequate solution to the problem of reducing belt wear in heavy bulk conveying situations, especially along the working and return flights. Efficiency is lost and maintenance becomes high when the complex carriage mechanisms becomes misaligned with the associated conveyor belts. Significant labor and expense also becomes involved when disassembly is required for replacing worn parts. There remains a need, therefore, for a bulk material conveyor with load supporting mechanisms that will operate effectively and that may be easily maintained to movably support a heavy bulk load along the working flight and become disengaged from the belt along the return flight, thereby reducing frictional contact and consequent belt wear. The invention disclosed herein is directed to a solution of the above problems and to fill the need for such apparatus.